Conventionally, in optical transmission systems, various determination methods of determining continuity of optical transmission paths such as optical fibers that connect between devices have been studied. As such a determination method, for example, a determination method using Fresnel reflection has been known.
In the determination method using Fresnel reflection, a level of signal light transmitted from an optical transmission apparatus to an optical receiving apparatus through an optical fiber, and a level of reflection light that reflects toward the optical transmission apparatus by Fresnel reflection caused by a break in an optical fiber or disconnection of an optical connector are compared. In the determination method using Fresnel reflection, continuity of an optical transmission path is determined based on a result of comparison between the level of the signal light and the level of the reflection light (Japanese Laid-open Patent Publication No. 05-128397).
However, in the conventional technique described above, there has been a problem that it is difficult to determine continuity of an optical transmission path accurately.
Specifically, in the conventional technique described above, even when an optical transmission path is conducting, when a flaw or an adherent is present on a surface of an end of a connector of the optical transmission path, it is considered that unexpected reflection light can occur by Fresnel reflection originated in the flaw or the adherent. In such a case, a level of signal light and a level of reflection light occurred by Fresnel reflection originated in the flaw or the adherent are compared in the conventional technique described above, it can be incorrectly determined that the optical transmission path is not conducting even though the optical transmission path is conducting.
On the other hand, in the conventional technique described above, when an optical transmission path is not conducting due to a break of an optical fiber, confusion occurs on a broken surface of the optical fiber, and it is considered that a level of reflection light is reduced by the confusion. In such a case, a level of a signal light and the level of the reflection light that is reduced by the confusion are compared in the conventional technique, and therefore, it can be incorrectly determined that the optical transmission path is conducting even though the optical transmission path is not conducting.